1. Field of the Invention
The present invention is related to the production of dinitro-o-alkylphenols and the purification of precursor o-alkylphenols.
2. Description of the Prior Art
Dinitro-o-sec-butylphenol is a commercial herbicide. It can be made by reacting o-sec-butylphenol with concentrated sulfuric acid to form a sulfonated o-sec-butylphenol which can be reacted with aqueous sodium nitrate to form mainly 2,4-dinitro-6-sec-alkylphenol. This reaction sequence as applied to higher alkylphenols is described in U.S. Pat. No. 2,810,767. It is also known to use nitric acid in place of the aqueous sodium nitrate as the nitrating agent.
Although the above reaction sequence works well with highly purified colorless o-sec-butylphenol, it is not completely satisfactory with less pure o-sec-butylphenol which is slightly yellow to amber or brown in color. With such impure o-sec-butylphenol starting material, the final dried product after the nitration is dark in color and contains a tar-like residue. Thus, a need exists to render impure o-sec-butylphenol satisfactory for sulfonation and nitration without an expensive purification procedure.
The various o-alkylphenols made by various methods often contain impurities which may result in the formation of undersirable by-products, especially tars. One such method which may result in the production of an o-alkylphenol containing a material which results in the production of tars when processed to make dinitro-o-sec-butylphenol as described above is the orthoalkylation of phenol with butene using an aluminum phenoxide or gammalaumina catalyst. One such process for preparing such an o-alkylphenol is described in U.S. Pat. No. 2,831,898.